12.2 Upgrade Feature (Oracle does not call it a bug) - /etc/oratab is alieved of it's contents

Be aware that if you apply any RU patch to 12.2, starting with the October 2017 RU, you will find that some contents of the oratab file might be removed.

For example, before I applied the January 2018 RU to a 12.2 base GI software home. Before the patch my oratab looked like this:

+ASM1:/app/grid/product/11.2.0.4/gi_1:N         # line added by Agent
sbx3db:/app/oracle/database/product/11.2.0.4/db_1:N             # line added by Agent

after the patch had been applied, the oratab was blank!

The lines that will be removed are any that end with # line added by Agent.
Oracle explains this "feature" in support document 2329359.1 - though not fully to my satisfaction. Essentially they blame this new functionality on changed ASM behaviors:

Note that this is the result of a change introduced in the 10/2017 RU. Since RU's are cumulative, you will see this change continuing in future RU's.